A crash course in septic systems and how they’re damaging the environment

Septic System

In his State of the State Address on February 3, 2011, Maryland Governor Martin O’Malley made the following statement:

“We must realize that where we choose to sleep, eat, and live affects our environment and it affects our Bay. Together, we’ve made some great progress in recent years. And we shouldn’t take that lightly. It didn’t happen by chance, it happened by choice … reducing farm run-off, reducing pollution from aging sewage treatment plants; most recently, starting to reduce the damage and the pollution that’s caused by storm-water run-off. But among the big four causes of pollution in the Bay, there is one area of reducing pollution where so far we have totally failed, and in fact it’s actually gotten much worse, and that is pollution from the proliferation of septic systems throughout our State – systems which by their very design are intended to leak sewage ultimately into our Bay and into our water tables.

Now look, you and I can turn around this damaging trend by banning the further installation of septic systems in major new Maryland housing developments. This is common sense, this is urgently needed, this is timely, and for the health of the Bay we need to do what several rural counties have already done and had the good sense to do.  We are up to this” (source).

Reactions to this statement have been mixed and confused.  If you’re not familiar with septic systems, the Governor has just informed you that they are designed to leak sewage.  How can this be true?  Who would design such a system?  If you’re one of the 420,000 Maryland households using a septic system you probably feel singled out.  You no doubt wonder how your perfectly functioning septic tank could be contributing to the death of the Chesapeake Bay (source).

In response to this confusion, I decided to do some digging and learn more about how septic tanks function, malfunction, and ultimately impact our waterbodies.  Hopefully this will shed some light on the issue and promote a better understanding of septic system developments.

How does a septic system work?

typical septic tank

Septic systems are installed on houses too far away to be connected to a wastewater treatment plant.  When properly installed and maintained, they are capable of handling all the waste you send down your drains by holding the waste onsite until it can be broken down by naturally occurring microorganisms.  Inside the septic tank waste naturally separates into three layers known as scum, wastewater, and sludge.  The wastewater is drained from the septic tank into a drainfield (located downhill from the tank).

Septic system drainfield

A drainfield is made up of one or more perforated pipes buried underground.  This allows wastewater to exit the system and be adsorbed by the soil and further decomposed by microorganisms. This process removes disease-causing organisms, organic matter, and most nutrients. The purified wastewater then either moves to the ground water or evaporates from the soil (source).  The other two layers – scum and sludge – are retained in the septic tank until they are removed via routine maintenance.

Wait, what do you mean by “maintenance”?

Like so much infrastructure in the United States, we are great at building it but tend to be somewhat lax when it comes to maintaining it.  This is especially true when the infrastructure in question is out of sight and inspections are unregulated.  Therefore, I’m not surprised when people I’ve spoken with tell me their septic systems are “self-maintaining” or only need maintenance every 20 years.  Nothing could be further from the truth, unless you have an absolutely massive septic tank or we’re talking about your vacation home.

In order to function properly, septic systems need to be completely pumped out on a routine basis.  The frequency of pumping varies depending on many factors, but the system should at least be inspected every four years.  One blog I read recommended “political pumping,” which is defined as an inspection scheduled every year there’s a presidential election (source).

Nevertheless, I’ve had people tell me that they haven’t had their septic system inspected for ten or more years and they’ve never had a problem.  This brings up a key point in understanding septic systems and their impact on the environment.  A failing septic system can appear to be fully functional for a long time before a home starts to experience problems (like drains backing up or a basement full of raw sewage).  In the meantime, the environment suffers.

Functioning / non-functioning septic tank
Healthy Septic Tank vs. Clogged Septic Tank

For example, if sludge (the bottom layer of the tank) isn’t routinely pumped out, it builds up and decreases the capacity of the tank.  This means that wastewater stays in the tank for shorter periods of time and thus enters the drainfield too quickly and without being fully treated.  If sludge builds up enough, it too can start entering the drainfield.  This leads to raw sludge draining into the ground, something the system was not designed to handle.  The eventual result can be a complete failure of the drainfield.  More than likely, however, this goes unnoticed, as the owner ignorantly believes nothing is wrong until the entire system fails (source).

Is inspection and maintenance enough?

If we were only talking about one septic system, for example, a farmhouse in the middle of acres of agricultural land, then inspection and maintenance would be enough.  The problem is that far more homes rely on septic systems than our environment can naturally handle – even if they are all well maintained.  This is because of nitrate, the one nutrient septic systems are not designed to remove.

Nitrate is naturally occurring and an important part of the nitrogen cycle, however, human releases of nitrogen have disrupted the natural balance of this cycle.  The Maryland Department of Planning estimates that 7% of all nitrogen entering the Chesapeake Bay from Maryland comes from septic systems (source).  Soil typically absorbs very little nitrogen, so nitrates released by septic systems are transported into the water table through groundwater movement and rainfall events.  This migration from the drainfield to the water table can take several years and therefore may not be immediately observable (source).  There are some septic systems capable of reducing nitrogen but that technology is generally expensive and most homes do not use it.

What effect does nitrogen have on water?

Nitrate in very high concentrations is toxic to humans and can render a water source unfit for human use.  This can occur when too many homes rely on both wells and septic systems in a confined area (source).  However, the problem the Bay is facing is more nuanced.  Elevated levels of nitrogen in our waterbodies cause algae blooms, as algae consume the excess nitrates in a process known as eutrophication (source).

Algae Bloom in the Chesapeake Bay
Algae Bloom in the Chesapeake Bay

As the algae blooms die off, the microorganisms that feed on them greatly reduce the amount of dissolved oxygen in the waterbody.  When dissolved oxygen levels fall below 30% saturation, the water becomes hypoxic and can no longer support fish and other aquatic species (source).  Large areas of hypoxia are known as dead zones and they occur frequently around the world wherever highly developed rivers empty into larger bodies of water – Most notably at the mouth of the Mississippi River and in the Chesapeake Bay  where they can cause massive fish kills (source).

Hypoxic dead zones around the globe
Hypoxic dead zones around the globe (from NASA) – click to see larger image


Even if you have a septic system in your backyard, your waste ends up in the same place as everybody else’s.  The key difference is that waste flowing to a wastewater treatment plant is more likely to be treated using biological nutrient removal (BNR) technology that dramatically reduces the amount of nitrogen before discharging into a receiving waterbody (source).  Your local wastewater treatment plant is also more likely to be routinely inspected and maintained than your neighbor’s septic system because there are laws that require it.

As for Governor O’Malley’s proposed ban on septic systems in new large housing developments, he’s facing some stern opposition from rural counties and building associations.  Prospectors who have been holding on to agricultural land in the hope of one day selling it to a developer for big bucks are waking up to find their ship may have already sailed.  New residential developments in the middle of nowhere aren’t possible without septic systems.  New growth may actually be focused in existing service districts, otherwise known as Maryland’s Smart Growth areas.  I thought it was funny today when a woman on WYPR (local NPR affiliate) referred to Smart Growth as something the state tried 15 years ago.  Actually, we’ve been trying it every year since; it’s just experienced very marginal success.  A septic system ban would be a huge step in the right direction.

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One thought on “A crash course in septic systems and how they’re damaging the environment”

  1. Thanks for the detailed post about linking sewage to pollution of the ocean.

    I would like to highlight the most significant issue –

    “As the algae blooms die off, the microorganisms that feed on them greatly reduce the amount of dissolved oxygen in the waterbody.”

    Why does the algae ‘die off’ ?
    Why is not consumed by zooplankton and fish ?

    We have a solution to cause Diatom Algae to grow.

    Diatoms are consumed by Zooplankton, finfish and crustaceans, so they do NOT die off and decompose.

    Thus the nutrients go up the food chain and water is clean and well oxygenated.

    Our solution is a simple substitution of algae that is not consumed by fish with algae that is consumed by fish.

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